The Tamron SP 500/8 and 350/5.6 also take 30.5mm filters in the rear.
They are less convienient than the Sigma. You have to remove the
adaptall, change filters, and remount the adaptall. The advantage may be
that there is no slip-in holder to lose. I used that Sigma issue to my
advantage by buying an EX+ Sigma missing its filter holder for $69 and
swapping the holder from the Nik*n mount 600 I inherited from my father.
For those who don't know, many long lenses use small filters in the back
of the optical path, but need piece of glass in place always to keep the
optical performance correct. They come with a clear or skylight filter
in place when new. I suspect other 3rd. party 500 mirror lenses use a
similar strategy.
If you read Gary's lens tests of the Zuiko and Tamron you will see that
sharpness differs by 1/3 letter grade, less than what he deems
significant in non-paired tests, have the same contrast rating and the
Zuiko is better on vignetting. IF you check here
<http://brashear.phys.appstate.edu/lhawkins/photo/mp-cat-tests.txt>, You
find the light fall-off of those 2 lenses and the Sigma to all be very
close. The Sigma wins on resolution which, combined given its longer
focal length, will resolve much more detail of a smaller subject area.
On balance, given the vagaries of testing and sample variability, I
don't see a lot of practical difference between these lenses other than
the possible joy of owning a Zuiko and possible pain of the cost of 72mm
filters. The Tamron is well made and the Sigma quite beautifully made.
Moose
Matt BenDaniel wrote:
The Zuiko can take a 72mm ND filter.
My Sigma takes a 30.5mm rear slip-in filter.
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